The inventors herein have developed an engine control methodology that allows efficient engine operation with some of the cylinders operating with more ignition timing retard than others. This allows the engine to operate at a higher engine load, thereby providing even more ability to retard ignition timing and generate heat for quick catalyst light-off.
However, the inventors have also recognized that such operation is only desired in certain operating modes, and in others, all of the engine cylinders should operate at optimum ignition timing for good fuel economy.